BACKUP & RECOVERYOption 1: Transaction Processing Systems

Backup & Recovery

Backup is the process of making a copy of data in case the original is lost or damaged.

Recovery is the opposite of the backup process where the backup copy of the data is restored and placed back on to the system.

Various procedures used to perform backups together with advantages and disadvantages.

Backup & Recovery

Backups provide a snapshot copy of data at particular points in time. A backup copy allows the systems data to be recovered back to the state it was at the precise moment the backup copy was made.

In the event of complete system failure that destroys the data completely, it is important to be able to recover to a point as close as possible to the time the failure occurred.

Backup & Recovery

The most common cause for a system failure requiring backup and recovery is hard drive failure. Specifically the read/write heads – being the moving parts of the drive.

Other issues include viruses, editing of previous files or hard/software configuration. To recover from most scenarios the approach to backup should be regular and kept for a reasonable time.

Frequency of backups and length of time stored is dependent entirely on the value of the data. Currently recreating 10MB of data can potentially cost a business $50,000 (inc. the cost of the system being inoperable). Additionally it is estimated that 43% of businesses who suffer severe or total loss of data never reopen.

Full and Partial Backups

There are three types of backups…

Full Partial – Incremental Partial – Differential

Backup & Recovery

Full Backup

Full backup, as it sounds, is a complete copy of ALL data within the system. This is a complete image of the entire hard disk, the operating system, configuration settings and all user data. Typically made weekly.

ADV’s – easiest to restore from complete failure DISADV’s – time, large amounts of storage

required

Backup & Recovery

Incremental Backup

Incremental Backup makes partial backups that copy all files that have changed or been created since the last backup. Incremental only includes files where the archive bit is true. Typically made daily.

ADV’s – faster than full DISADV’s – extra time required to recover data.

Often the last full followed by consequent incrementals.

Backup & Recovery

Differential Backup

Differential Backup uses partial backups to make copies of all files that have been altered since the last full backup. If made daily then they will contain copies of all files within all previous partial backups since the last full was made.

ADV’s – faster than full DISADV’s – extra time required to recover data.

Often the last full followed by consequent partial. Increasing file size leading up to next full backup.

Transaction Logs, Mirroring and Rollback

We said previously that transaction logs contain historical details of each transaction performed in a system – including transaction currently being processed. These details can be used to restore a system to a state at some precise point in time so that completed transaction can be recommitted or rolled back AND incomplete transactions can be continued or rolled back.

Come to page 416 for two examples of this…

Backup Media

Magnetic tape remains the dominant media for backing up data on large systems, including most TPS’s. This is due to large volume of storage, inexpensive per Gig and compared to alternate systems. That said the following could be utilised…

Backup Media

Complete the table above using page 416-417…

Media Brief descriptionMagnetic tapeHard diskCD

DVD

Online system

Backup Procedures

You should be careful not to utilise the same backup procedures continuously. Multiple types and sets of backup media should be purchased and used with the aim being to have as many complete backups copies produced in as many different times as possible. This way data can be recovered back to a variety of different past states.

Most backup procedures fail due to human error.

Backup Procedures

For example…

• Mr C’s laptop• Mr C’s Playstation 3• College tape backups• http://www.zdnet.com/how-one-busi

ness-recovered-from-a-raid-failure-7000025177/

Backup Procedures

In groups of 2-3 I want you to propose…

1. A backup system (with associated media) for HOME

2. A backup system (with associated media) for SCHOOL

______________________________________________

When you are finished you can play this

Backup Procedures

There are three approaches to backup that the syllabus talks about…

- Grandfather, Father, Son (GFS)- Round Robin- Towers of Hanoi

Backup Procedures

Grandfather, Father, Son

This is the most commonly used rotation scheme. GFS is as follows…

Daily Backups – SonWeekly Backups – FatherMonthly Backups - Grandfather

Full or partial backups are performed each working day to a son tape except for on a Friday. Every Friday (except the last of the month) a Father tape is used as a full backup for the week. On the last Friday of the month a grandfather backup is completed in full for the month.

Backup Procedures

Grandfather, Father, Son

The son tapes are reused each week, the set of father tapes are reused each month and the grandfather tapes are reused each year. Typically the monthly/grandfather tapes are stored offsite and weekly tapes are stored in a local location such as a safe.

Backup ProceduresMONDAY TUESDAY WEDNESD

AYTHURSDAY FRIDAY

Mon Tue Wed Thurs Week 1

Mon Tue Wed Thurs Week 2

Mon Tue Wed Thurs Week 3

Mon Tue Wed Thurs Month 1

Mon Tue Wed Thurs Week 1

Mon Tue Wed Thurs Week 2

Mon Tue Wed Thurs Week 3

Mon Tue Wed Thurs Month 2

Mon Tue Wed Thurs Week 1

Mon Tue Wed Thurs Week 2

Mon Tue Wed Thurs Week 3

Mon Tue Wed Thurs Month 3

There are 10 different tapes represented above for a 3 week GFS rotation. Come to page 420-421 for further detail…

Backup Procedures

Round Robin Backup

A round robin treats all tapes equally. Each tape is numbered sequentially for example on a Monday to Friday rotation there would be 5 tapes numbered 1-5. As tape 5 is used for backup tape 1 is reused and the cycle continues. Each tape added to the cycle extends the ability to restore a further day.

This is suitable for small businesses only and would typically look like 30 tapes on rotation over the course of a month. Full backups should be archived at regular intervals if using this method.

Backup Procedures

Towers of Hanoi

The Towers of Hanoi rotation is based on the game you played previously. To transfer this logic puzzle to a backup rotation each disk represents a tape and the order in which the disk are moved determines the order in which the tapes are moved. In the example on the next page (with 6 tapes) the complete sequence of movement takes 32 days.

Tapes used less often will contain data from the distant past whilst those used more often contain most recent data.

Backup Procedures

Towers of Hanoi with 6 tapes labelled A-E

Day 1 Day 2 Day 3 Day 4 Day 5 Day 6 Day 7 Day 8

A B A C A B A D

Day 9 Day 10

Day 11

Day 12

Day 13

Day 14

Day 15

Day 16

A B A C A B A E

Day 17

Day 18

Day 19

Day 20

Day 21

Day 22

Day 23

Day 24

A B A C A B A D

Day 25

Day 26

Day 27

Day 28

Day 29

Day 30

Day 31

Day 32

A B A C A B A F

Backup Procedures

Towers of Hanoi

The Towers of Hanoi requires specialized backup software that operates in conjunction with tape libraries. The software performs the daily tape rotation automatically loading and backing up the correct tape in the sequence. The same software is used to restore in the event of an issue over the course of the cycle.